1. Field of the Invention
The present invention generally relates to a method and an apparatus for inspecting an appearance of a bonding-wire. More specifically, the present invention is directed to a method and an apparatus for inspecting an appearance of a bonding-wire connecting between a semiconductor chip and a lead frame, for instance, suitably inspecting a height shift from a preset reference plane, and also a positional shift with a horizontal plane.
2. Description of the Related Art
Recently, semiconductor packages have a large number of pins and are made thinner. Such demands are made that pitches between pins should be narrowed and longer bonding-wires are required in the wire bonding techniques for connecting semiconductor chips with lead frames. As a consequence, severe managements are necessarily required as to the loop shapes of the bonding-wires, and therefore the appearance inspection of the bonding-wire status are very important.
Conventionally, these types of bonding-wires appearance inspecting apparatuses are disclosed in, for instance, U.S. Pat. No. 4,874,956 issued on Oct. 17, 1989, Japanese Laid-Open Patent Applications Nos. Hei 4-273006 (Sep. 29, 1992) and Hei 5-175312 (Jul. 13, 1993). Then, this conventional bonding-wire appearance inspecting apparatus disclosed in Japanese Laid-open Patent Application No. Hei 5-175132 will now be described with reference to FIG. 1 and FIG. 2.
In the bonding-wire appearance inspecting apparatus shown in FIG. 1, a bonding-wire 102 is illuminated by an illumination device 101, and the reflection/scattered light from the bonding-wire 102 is imaged by an imaging device 103 mounted above the bonding-wire 102 along the vertical direction. Based on the image signal obtained from the imaging device 103, the focusing coincidence degree of the image signal is processed to obtain the numeral value by the image processing device 104. The imaging device 103 is mounted on a focus controlling device 105 to control the height. Then, while changing the height of the imaging device 103, the bonding-wire 102 is imaged to calculate the focus coincidence degree of the resulting image signal. For instance, as shown in FIG. 2, a plurality of heights F1 to F5 are preset, and the imaging device 103 is transported to image the bonding-wire 102 in such a manner that a focusing element 103a in the imaging device 103 can be focused at the respective heights F1 to F5. Then, the three-dimensional shape of the bonding-wire 102 is calculated by the central processing unit 106 based upon the focus coincidence degree calculated by the image processing device 104 and the height information of the imaging device 103 obtained from the focus control device 105. This three-dimensional shape calculation of the bonding-wire 102 is performed for all of plural bonding-wires 102 on a X-Y stage 107 by transporting the X-Y. stage on which these bonding-wires, 102 are mounted. The information indicative of the calculated three-dimensional shape of this bonding-wire 102 is displayed on a display device 108.
In this conventional bonding-wire appearance inspecting apparatus, a plurality of images for the same bonding-wire must be acquired, while changing the focus positions of the imaging device 103. As a consequence, very lengthy time to input image data is required to detect the height of the bonding-wire 102. Also, since a large number of images must be processed, very complex image processing operations must be carried out.
Further, when the bonding-wire 102 is largely inclined, the reflection light from this inclined bonding-wire cannot be sufficiently detected by the imaging device 103. As a result, the appearance of the inclined bonding-wire 102 could not be inspected in high precision.
Moreover, since this conventional inspecting apparatus is equipped with no means for imaging two-dimensionally whole the semiconductor chip with the bonding-wire, the positional shift of the bonding-wire within the horizontal plane could not be inspected in high precision nor in high speed.